The technical field is digital memory arrays, particularly a method and apparatus for sensing the state of data cells in a digital memory array.
Many consumer devices are now constructed to generate and/or use large quantities of digital data. Portable digital cameras for still and/or moving pictures, for example, generate large amounts of digital data representing images. Each digital image may require several megabytes of data storage, and such storage normally must be available in the camera.
Data storage devices comprising cross-point memory arrays are one form of storage applicable for portable devices such as digital cameras. A plurality of the memory arrays may be stacked and laminated into a memory module providing inexpensive, high capacity data storage. The memory module can be employed in an archival data storage system in which the memory module provides a write-once data storage unit receivable in an appliance or interface card.
Cross-point memory arrays comprise sets of transverse electrodes, also known as row and column lines, with memory elements formed at each cross-point of the electrodes. Each memory element can be switched between low and high impedance states, representing binary data states, by application of a write signal in the form of a predetermined current density through the memory element. Each row and column line is coupled to a sensing diode that enables sensing, or reading, of the state of the memory element corresponding to the row or column line. A single sense line spans all of the row or column lines and draws leakage current from all of the sense diodes except for the single sense diode connected to the addressed row or column line. The leakage current flows in a direction opposite to the sense current and can be many times larger than the sense current. Therefore, the leakage current may hide the sense current, making it difficult to accurately sense the state of the addressed memory element.
Therefore, a need exists for a method and apparatus for sensing the state of data cells in a cross-point memory array that reduces the effect of leakage current on the sense current thereby allowing the sense current to be more easily detected.
A memory storage device comprises a cross-point memory array including a first and second set of transverse electrodes that intersect at a plurality of cross-points. A memory element is located at each cross-point, and each memory element is switchable between a low and a high impedance state. Address decoding circuitry is coupled to the first and second set of transverse electrodes. Striping circuitry is coupled to the first set of transverse electrodes, which are grouped together to form a set of stripes. Each of a plurality of sense line segments is coupled to a separate stripe by a diode, and a sense bus is coupled to each diode.
A memory storage device comprises a cross-point memory array including a first and second set of transverse electrodes that intersect at a plurality of cross-points. A memory element is located at each cross-point, and each memory element is switchable between a low and a high impedance state. Address decoding circuitry is coupled to the first and second set of transverse electrodes. Striping circuitry is coupled to the first set and second set of transverse electrodes, where each set of electrodes is grouped together to form a first and second set of stripes. Each of a plurality of sense line segments is coupled to a separate stripe by a diode. A first sense bus is coupled to each diode that is coupled to the first set of stripes, and a second sense bus is coupled to each diode that is coupled to the second set of stripes.
A method for sensing the state of a memory element in a memory storage device includes the step of coupling striping circuitry to a first set of transverse electrodes, where the first set of transverse electrodes is grouped together to form a set of stripes. The method also includes the steps of generating a current along a selected electrode corresponding to the memory element and detecting whether the current flows in the selected electrode.